Morton neuroma

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Definition: Morton’s neuroma is a benign neuroma of an intermetatarsal plantar nerve, most commonly of the second and third intermetatarsal spaces (between 2nd-3rd and 3rd-4th metatarsal heads).This problem is characterised by pain and/or numbness, sometimes relieved by removing footwear.

Despite the name, the condition was first correctly described by a chiropodist named Durlacher, and although it is labeled a "neuroma", many sources do not consider it a true tumor, but rather a perineural fibroma (fibrous tissue formation around nerve tissue).

Histopathology

Microscopically, the affected nerve is markedly distorted, with extensive concentric perineural fibrosis.

The arterioles are thickened and occlusion by thrombi are occasionally present.

Perineural thickening without evidence of fibroblastic proliferation could be demonstrated, together with an intraneural deposition of an amorphous substance.

In some patients suffering from Morton’s disease for a longer time, a more pronounced epineural thickening in the pre-stenotic zone could be shown, with partial replacement of nerve fibers by amorphous substance. Endoneural fibrositis can be seen at the level of the stenosis.

Electron-microscopy in patients after one year showed an increase in collagenous endoneural fibers and microfibrils.

These histopathological findings suggest a compressive mechanism in the pathogenesis of the damage to the common interdigital nerve in Morton’s disease, caused by the extrinsic anatomical structures surrounding the nerve.

The so-called "neuroma" can be identified with the pre-stenotic swelling.

References

 [Morton’s disease: optic and electron microscopy observations]. De Palma L, Tulli A.
Acta Orthop Belg. 1991;57(3):285-95. French. PMID: 1950513

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